Automatic-spark advance mechanism



1962 K. s. JOHNSON ETAL 3,051,150

AUTOMATIC SPARK ADVANCE MECHANISM Filed Jan. 51, 1961 5 Sheets-Sheet lINVENTORS K41. //v 5. Jd /A/SO/V &

05 527 /C Fem K MAN Aug. 28, 1962 K. s. JOHNSON ETAL 3,051,150

AUTOMATIC SPARK ADVANCE MECHANISM Filed Jan. 31, 1961 5 Sheets-Sheet 2Aug. 28, 1962 K. s. JOHNSON ET AL AUTOMATIC SPARK ADVANCE MECHANISM sSheets-Sheet 5 Filed Jan. 31, 1961 INVENTORS K4 L//\/ 5 JbH/VSO/V 2BY/POBE/PT F/PA/VK Q 031% ATTORNEY res Parent 3,951,158 Patented Aug.28, 1962 This invention relates generally to ignition distributors forinternal combustion engines, and more specifically to those ignitiondistributors wherein the advance mechanism is controlled in accordancewith engine manifold and carburetor venturi vacuums, commonly referredto as full pressure distributors.

Full pressure distributors usually employ a flexible diaphragm, which issecured to a movable breaker plate and positioned by both the eng'nemanifold vacuum and venturi vacuum. Springs are also provided forpurposes of calibration by resisting the movement of the diaphragm.

In order to obtain smooth engine idling, maximum retardation of theignition is usually necessary while slight opening of the throttlerequires some advance of the ignition timing. This general proposition,however, does not hold true for all engine operating conditions. Thatis, for example, during heavy load, low speed engine operatingconditions, a retard of the ignition timing is desirable in order toprevent undesirable detonation.

Accordingly, in order to accomplish the above, it has become acceptedpractice to provide what is commonly referred to as a spark valve incooperation with the ignition distributor and carburetor. The sparkvalve is usually comprised of a valve member positioned in accordancewith vacuum responsive means so as to at times allow communicationbetween a source of engine manifold vacuum and the flexible diaphragm ofthe ignition distributor.

The vacuum responsive means is made sensitive to the manifold vacuum soas to allow the above communication only after a predetermined minimumvalue of manifold vacuum has been attained. The accepted procedure indetermining the value of manifold vacuum is by the provision of apre-loaded spring which is so placed as to oppose the movement of thevacuum responsive means in the valve opening direction.

Ignition systems constructed in accordance with the above are,nevertheless, still deficient in at least one respect. That is, once thevalue of the manifold vacuum for opening the spark valve has beenselected, there is no way of changing the point at which the spark valvewill open. In other words, by selecting one such value, optimum engineperformance is often sacrificed in at least some areas of the overallengine operating range.

Accordingly, it is now proposed to provide means for varying thepredetermined value of manifold vacuum required for opening the sparkvalve in accordance with engine load.

More specifically an object of this invention is to provide meansresponsive to throttle valve position for varying the point at which thespark valve will allow communication between a source of engine manifoldvacuum and flexible diaphragm which is the immediate control over theignition timing.

Other objects and advantages will become apparent when reference is madeto the following written description and accompanying drawings wherein:

FIGURE 1 is a fragmentary cross-sectional view of a carburetorconstructed generally in accordance with the teachings of the inventionand cooperating with an ignition distributor;

FIGURE 2 is a graph illustrating the relationship between spark vacuumand engine speed;

FIGURE 3 is a graph illustrating the relationship between degrees ofignition advance and engine speed;

FIGURE 4 is a fragmentary cross-sectional view of a modification of theinvention;

FIGURE 5 is a cross-sectional view, partially illustrated in schematicform, of another modification of the invention.

Referring now in greater detail to the drawings, FIG- URE 1 illustratesa carburetor 10 having an induction passage 12 with a throttle valve 14therein controlling the flow therethrough to the intake manifold 16 ofthe engine. An actuating lever 18 may be suitably secured to thethrottle shaft 22, and a rod 20 and spring 24 may be provided tocooperate with lever 18 for positioning the throttle valve.

The ignition distributor 26 may be comprised generally of a housing 28having provision therein for the reception of a driving shaft to which acam 30 is secured so as to rotate therewith. A breaker plate 32 mountedon a suitable bearing member is adapted to rotateabout the driving shaftand cam 30. The breaker plate 32 carries thereon a breaker arm assembly34 which includes a cam engaging portion 36 'engageable by the rotatingcam 30 to efiect the make and break of the ignition circuit at thecontacts indicated at 38. The cam 30 and the shaft on which it ismounted are, of course, rotated in timed relation with the engine bymeans of any transmission means well known in the art.

The distributor advance mechanism is controlled generally by thepressure responsive device 40 which commum'cates by means of suitableconduitry with ports 42 and 44 in the carburetor 10 so as to senseengine manifold and carburetor venturi vacuum, respectively.

The pressure responsive device 40 may be substantially comprised of ahousing 46, and a cover member 48 rigidly held together in a manner soas to peripherally secure a diaphragm member 50 therebetween. A member52, connected at its one end to the diaphragm member 50', is adaptedtobe operatively engaged with the breaker plate 32, as by means of ahole formed therein for the reception of the end 54 of member 52. Anysuitable retaining means suchas a cotter pin 56 may be employed so as toprevent accidental disengagement between member 52 and the breaker plate32. Chamber 58 formed generally by "cover 48 and diaphragm 50 is exposedto a. source of vacuum, while the chamber 60 is vented to theatmosphere. The entire pressure responsive device may, of course, besecured to the housing 28 by any suitable means such as screws 62.

Calibration springs 64 and 66 are secured at one end to the anchor pins68 and 70, which in turn are fixedly secured to the housing 28. Theother ends of springs 64 and 66 are connected to the breaker platespring posts 72 and 74. Openings 76 and 78 may of course be formed inthe breaker plate 32 in order to provide the necessary clearance foranchor pins 68 and 70.

Other portions of the distributor such as the distributing rotor, upperdistributor cap and various output terminals are neither shown nordescribed, since they form no part of this invention and are well knownto those skilled in the art.

Valving means illustrated generally at 80 are provided in order tocontrol the engine manifold vacuum which is ultimately communicated tochamber 58 through restriction 144. The Valving means is comprised oftwo independently actuated valve assemblies 82 and 84, which may becontained within the general structure of the carburetor body '11 if sodesired.

Valve assembly 84, which may be threadably received within the chamber88, is comprised of a housing portion 104 which cooperates with a covermember 106 to pcripherally secure a pressure responsive diaphragm memher108 therebetween. Chamber 110, formed generally by the diaphragm 108 andcover 106 is ventedto the atmosphere, as by ports 112, while chamber 114on the opposite side of the diaphragm isin communication with theinduction passage 12 by means of port 42, conduit 116 and radiallyformed passages 118 in the housing '104.

An orifice 120 formed in housing 104 provides communication at timesbetweenchambers 88 and 114, depending upon the position of valve member122, which has its one end 124 connected to'the diaphragm 108 so 'as tobe moved therewith. Spring 126 and adjusting member 128 are provided soasto enable selection of the particular vacuum value at which valvemember 122 will be moved to the left and orifice 120 will be opened.

The throttle shaft 22 has a cam member 90 secured thereto which isadapted to be in constant contact with end 92 of the valve member 94which comprise valve assembly 82. Valve member 94 is s'lidably receivedWithin body portion 1 1 and is urged to the left by both springs 126 and96. An adjustable member 98 is also provided in order to vary theinitial force of spring 96..

The other end of member 94 has a spring abutment portion 130 formedthereon against which spring 126 normally urges. Additionally, a passage132 is provided so as m at times allow communication between chamber 88and conduit 134 which is in communication with conduit 116. Arestriction 136 may be provided in conduit 116 while restriction 138isprovided in conduit 140 which continually communicates between chamber88 and conduit 116.

A conduit 142, including a restriction 144 therein, communicates betweenchamber 88 and conduit 146 which leads from port 44 to chamber 58 of thepressure responsive device 40.

Operation Referring to FIGURE 1, let it be assumed that the engine isrunning at curb idle and the spark advance mechanism is in full retard.Under these conditions, the elernents would assume positions asillustrated in FIG- URE 1. r

Springs 64 and 66, being anchored at one end to the housing 28 by meansof anchor pins 68 and 70, respectively, and connected to theirrespective other ends to the breaker plate spring posts 72 and 74, urgethe breaker plate 32 clockwise about the distributor shaft and cam 30until the holes 76 and 7 8 abut against the anchor pins 68 and 70. Thiscauses the breaker arm assembly 34 to be rotated to a position wherebythe cam 30 will contact the cam engaging portion 36 at a time when therespective pistons within the engine are most nearly at top dead center.

If the throttle valve 14 is moved to wide open position, the air flowpast the venturi 148 causes a venturi vacuum at port 44 which isdirected generally by means of conduit 146 to chamber 58. As enginespeed increases with the throttle valve maintained at wide openposition, the venturi vacuum increases, causing the diaphragm 50 to bemoved in ever increasing amounts to the left thereby rotating thebreaker plate 32 and the breaker arm assembly counter-clockwise aboutcam 30. This in turn causes the cam 30 to engage the cam engagingportion 36 at ever increasing degrees of engine crankshaft rotationahead of when the engine pistons reach top dead center. This is 'usuallyreferred to by those skilled in the art as degrees of ignition advance.

It should be noted that during this period of wide open throttleoperation, the throttle shaft 22, by virtue of the action of its camportion 90 during the last few degrees of movement towards wide openthrottle position, has allowed'valve member 94 to be moved to the leftby the cooperative action of springs 96 and 126. As a consequence aresults in a bleedingreffect causing a diminution of the 'venturi vacuumas sensed by diaphragm 50 and continuing to do so whenever the valvemember 94 has placed passage 132 in juxtaposition with conduit 134.

In view of the above, itbecomes apparent that lighter calibratingsprings 64 and 66 may be employed; this is because the eifective forceopposing them and created by the venturi vacuum has been materiallydiminished by causing passage 132 to communicate between conduits 134and 142 so as to allow atmospheric pressure to bleed off the venturivacuum.

If, for example, the throttle valve were opened slowly from its fullyclosed position to some part throttle position as required by normalroad loads, the valve member 94 would not have moved sufliciently toallow communication through passage 132 and po1t'42 would be exposed tomanifold vacuum. I

The existing manifold vacuum would then be communicated by means ofconduits 116 and 118 to chamber 114, causing the diaphragm 138 and valve122 to move to the left. Since, as stated previously, the passage 132 isclosed, the manifold vacuum is directed through restriction 144 tochamber 58 causing an increase in ignition advance. As a result of theprovision of lighter or weaker calibrating springs, there is lessresistance oifered to the movement of the diaphragm 50, and consequentlygreater ignition advances at part throttle engine operating conditionsis obtainable than with prior conventional ignition systems.

A separate conduit 149, including a restriction 138 therein, may beprovided so as to continually communicate a small degree of manifoldvacuum to conduit 142 during those periods of engine operation whereinthe manifold vacuum as yet is insufficient to fully open valve 122against the action of spring 126. The basic operation of the inventionis the same; the primary distinction is that in the absence of apassagesuch as conduit 144), no communication of manifold vacuum from port 42to conduit 142 is possible until that predetermined value of manifoldvacuum is attained which will completely open valve 122.

Another important feature of the invention is the provision of meanswhereby the predetermined value of manifold vacuum necessary to openvalve 122 can be varied in accordance with engine load. This isaccomplished generally by the cooperative action of valve assembly 84and members 22, and 94.

For example, with the elements in the positions illustrated by FIGURE 1,spring 126 may possibly be compressed so as to exert a force of onepound in a direction closing the valve 122, whereas when the throttle 14is moved to half wide-open position the force of spring 126 may bereduced to possibly 0.75 pound. The exact forces are of course a matterof design and the variation as between any two throttle positions willbe determined by the particular contour employed on cam member 90.

' Consequently, since the force of spring 126 can be varied inaccordance with throttle valve position, that is, engine load, itbecomes apparent that at certain times a lesser pressure difierentialacross diaphragm 1118 is required to open valve 122 than at other times.This of course means that, depending on engine load or throttle valveposition, the valve 122 will open at infinite numbers of distinctlydiiferent values of manifold vacuum.

FIGURE 2 is a graph which illustrates the relationship between sparkvacuum and engine speed, By spark vacuum is meant the actual vacuumsensed by the diaphragm member 50. Curves B through G are obtained byrunning the engine at a constant manifold vacuum and the numbers, 2through 14, on curves B through G represent the manifold vacuum value interms of inches of mercury (Hg). Curve Ais of course a low variablemanifold vacuum curve, that being obtained by running the engine at wideopenthrottle (W.O'.T.).

The second set of curves labeled H through L represent the spark vacuumobtainable at different fixed throttle openings wherein the load on theengine is varied in order to increase or decrease engine speed. Thenumbers through 60 represent the degrees of throttle opening from closedthrottle position.

As was stated previously, usually during periods of heavy load, lowspeed engine operation a retard of the ignition timing is desirable inorder to prevent undesirable detonation. The conventional distributorwould have spark advance curves similar to curves R, S, T, U, and V, ofFIGURE 3 which result in ignition advances of approximately 6, 13 18,22, and 27, respectively at 900 rpm. However, in a particular engine itmay be determined that at 10 throttle opening, at an engine speed ofapproximately 900 rpm. and at 20 throttle opening, at an engine speed of1400 rpm. and at 40 throttle opening, at an engine speed of 1900 r.p.m.no ignition advance due to manifold vacuum is desired because such wouldresult in undesirable detonation. in other words, the combinationsrepresented beneath and to the left of line X of FIGURE 2 areundesirable.

The invention now provides means whereby the above can be accomplished.That is, the throttle valve position is indicated to the valve assembly84 by means of cam 90, member 94 and spring 126. It should be noted thatat closed throttle position the force of spring 126 closing valve member122 is the greatest and that progressive opening of the throttle resultsin the lessening of the spring force on valve 122. This in turndetermines when valve 122 will open and communicate the then-existingmanifold vacuum to diaphragm member 50.

Consequently, by properly contouring the cam member 90, it is possibleto obtain ignition advance curves represented by curves M, N, O, P, Qand R or" FIGURE 3 instead of those represented by S, T, U and V. Itshould be noted that at heavy load, low engine speed operation noappreciable ignition advance due to manifold Vacuum is realized.

As was previously stated, conduit 14% and restriction 133 may beprovided as illustrated if desired. However, its use is not necessary inorder to practice the invention. It a conduit similar to conduit 14% isnot employed, no communication of manifold vacuum from port 42 toconduit 142 is possible until that predetermined value of manifoldvacuum is attained which will completely open valve 122, against theforce of spring 126.

Just as conduit 149, so'may conduits 132 and 134 be eliminated alongwith restriction 136. This construction is illustrated by FIGURE 4. Allelements which are like or similar to those of FIGURE 1 are identifiedwith like reference numbers. It should be noted that element 94 does notcontain a passage 132 as previously illustrated in FIGURE 1, nor does apassage functionally similar to conduit 134 exist. The sole purpose ofelement 94, in the embodiment of FIGURE 4, is to vary the force ofspring 126.

However, the function of conduits 132 and 134, as previously described,can nevertheless be retained by the provision of spring retainers 158and 161 That is, the cam 90 may be contoured so as to allow, atsubstantially wide-open throttle conditions, member 94 to be movedsufficiently to the left by spring 96 so as to open valve 122. In otherwords, member 94 Will move a sufficient amount to place the normallycompressed spring 126 in somewhat of a state of tension thereby pullingvalve 122 open. 1

The embodiment disclosed by FIGURE 5 is structurally similar andfunctionally identical to that disclosed by FIGURE 4. All elements whichare like or similar to those of FIGURES 1 and 4 are identified with likereference numbers. Member 150, which is in contact with cam member 90,has a threaded portion thereon adapted to receive a coacting springabutment member 152. The spring 154, placed intermediate member 152 anddiaphragm 108, transmits the movements of cam 90 as a force opposing theforce ofspring 126. That is, assuming that spring 126 has a force of 1.0lb. on valve 122 in the position shown, it becomes evident that as cam98 is rotated in the throttle opening direction that spring 154 iscaused to be increasingly compressed and that the net efifective forceof spring 126 tending to keep valve 122 closed, has been diminished byan amount equal to the increase in compression of spring 154.

Member 151? may of course be constructed of a length suitable forpositively opening the valve 122 against the force of spring 126. Thatis, during periods of, for example, wide open throttle operation, it maybe desirable to fully open valve 122. Accordingly, this can beaccomplished by having end 156 of member abut against member 124 in amanner so as to forcibly move the valve 122 to the right thereby openingconduit 121) and allowing communication between conduits 116 and 142.

Although but three embodiments of the invention have been disclosed anddescribed, it is apparent that other modifications of the invention arepossible within the scope of the appended claims.

What we claim as our invention is:

1. An ignition system for an internal combustion engine having aninduction passage with a throttle valve controlling the flow of airtherethrough, comprising an ignition distributor having a housing, aswitch in said housing, a cam member normally rotatable in accordancewith engine speed and adapted to intermittently open said switch foreffecting a make and break of the ignition circuit, a breaker platenormally supporting said switch and having relative angular motion withrespect to said housing, pressure responsive means secured to saidhousing and operatively connected to said breaker plate for rotatingsaid breaker plate in accordance with engine requirements, a venturiformed in said induction passage upstream of said throttle valve, firstconduit means communicating between the throat of said venturi and saidpressure responsive means, second conduit means communicating betweensaid induction passage at a point upstream of said throttle valve whensaid throttle valve is in its normally closed position and said firstconduit means, first valve means connected serially in said secondconduit means and adapted to at times control the communication throughsaid second conduit means, said first valve means comprising a diaphragmmember, a valve member secured to said diaphragm member and adapted tobe positioned thereby, said diaphragm member being responsive to thevacuum sensed by said second conduit means at its point of communicationwith said induction passage and effective to move said valve member inthe opening direction upon the attainment of a predetermined vacuumvalue, third conduit means connected in parallel with said secondconduit means so as to bypass said first valve means, a variablypositioned abutment member, spring means connecting said abutment memberand said valve member to each other, a cam member rotatably positionedin accordance with the position of said throttle valve, second springmeans continually urging said abutment member against said cam member,said cam member and abutment member being eflfective to vary the forceof said first mentioned spring means so as to vary said predeterminedvacuum value required to open said valve member.

2. An ignition system for an internal combustion engine having aninduction passage with a throttle valve controlling the flow of airtherethrough, comprising an ignition distributor having a housing, aswitch in said housing, a cam member normally rotatable in accordancewith engine speed and adapted to intermittently open said switch forefiEecting a make and break of the ignition circuit, a breaker platenormally supporting said switch and having relative angular motion withrespect to said housing; pressure responsive means secured to saidhousing and operatively connected to said breaker plate for rotatingsaid breaker plate in accordance with engine requirements, a venturiformed in said induction passage upstream of said throttle valve, firstconduit means communicating between the throat of said venturi. and saidpressure responsive means, second conduit means communicating betweensaid induction passage at a point upstream of said throttle valve whensaid throttle valve is in its normally a variably positioned abutmentmember, spring means connecting said abutment member and said valvemember to each other, a cam member rotatably positioned in accordancewith the position of said throttle valve, second spring meanscontinually urging said abutment member against said cam member, saidcam member and abutment member being efiective to vary the force of saidfirst mentioned spring means so as to vary said predetermined vacuumvalue required to open said valve member.

3. An ignition system for an internal combustion engine having aninduction passage with a throttle valve controlling the flow of airtherethrough, comprising an ignition distributor having a housing, aswitch in said housing, a cam member normally rotatable in accordancewith engine speed and adapted to intermittently open said switchforeiliecting a make and break of the ignition circuit, a breaker platenormally supporting said switch and having relative angular motion withrespect to said housing, pressure responsive means secured to saidhousing and operatively connected to said breaker plate for rotatingsaid breaker plate in accordance with engine requirements, a venturiformed in said induction passage upstream of said throttle valve, firstconduit means communicating between the throat of said venturi and saidpressure responsive means, second conduit means communicating betweensaid induction passage at a point upstream of said throttle valve whensaid throttle valve is in its normally closed position and said firstconduit mined vacuum value, third conduit means connected in parallelwith said second conduit means so as to bypass said first valve means, avariably positioned abutment member, spring means connecting saidabutment member and said valve member to each other, a cam memberrotatably positioned in accordance with theposition of said throttlevalve, second spring means continually urging sadi abutment memberagainst said cam member, said cam member and abutment memberbeingeffective to vary the force of said first mentioned spring means so asto vary said predetermined vacuum value required to open said valvemember, fourth conduit means having its one end in continualcommunication with said second conduit means at a point between saidfirst valve means and said induction passage, second valve means for attimes connecting the other end of said fourth conduit means to saidsecond conduit means so as to bypass said first valve means, and meansresponsive to the position of said throttle valve and operative duringperiods of substantially wide open throttle operation for causing said 8second valve means to complete the communication between said other endof said fourth conduit means and said second conduit means. 7

4. An ignition system for an internal combustion engine having aninduction passage with a throttle valve controlling the flow of airtherethrough, comprising an ignition distributor having a housing, aswitch in said housing, a cam member normally rotatable in accordancewith engine speed and adapted to intermittently open said switch forefiecting a make and break of the ignition circuit, a breaker platenormally supporting said switch and having relative angular motion withrespect to said housing, pressure responsive means secured to saidhousing and operatively connected to said breaker plate for rotatingsaid breaker plate in accordance with engine requirernents, a venturiformed in said induction passage upstream of said throttle valve, firstconduit means communicating between the throat of said venturi and saidpressure responsive means, second conduit means commuriicating betweensaid induction passage at a point upstream of said throttle valve whensaid throttle valve is in its normally closed position and said firstconduit means, first valve means connected serially in said secondconduit means adapted to at times control the communication through saidsecond conduit means, said first valve means comprising a diaphragmmember, a valve member secured to said diaphragm member and adapted tobe positioned thereby, said diaphragm member being responsive to thevacuum sensed by said second conduit means at its point of communicationwith said induction passage and effective to move said valve member inthe opening direction upon the attainment of a predetermined vacuumvalue, a variably positioned abutment member, spring means connectingsaid abutment member and said valve member to each other, a cam memberrotatably positioned in accordance with the position of said throttlevalve, second spring means continually urging said abutment memberagainst said cam member, said cam member and abutment member beingefiective to vary the force of said first mentioned spring means so asto Vary said predetermined vacuum value required to open said valvemember, third conduit means having its one end in continualcommunication with said second conduit means at a point between saidfirst valve means and said induction passage, second valve means for attimes connecting the other end of said third conduit means to saidsecond conduit means so as to bypass said first valve means, and meansresponsive to the position or said throttle valve and operative duringperiods of substantially wide open throttle operation for causing saidsecond valve means to complete the communication between said other endof said third conduit means and said second conduit means.

5. In an ignition system for an internal combustion engine having aninduction passage with a throttle valve controlling the flow of airtherethrough, the combination of an ignition distributor includingtiming means therein for controlling the timing of ignition, vacuumresponsive means for positioning said timing means, means for creating afirst vacuum in accordance with the velocity of air flow through saidinduction passage, means for transmitting said first vacuum to saidvacuum responsive means, engine vacuum responsive valve means for attimes directing engine vacuum to said vacuum responsive means,

resilient means biasing said valve means in the closing direction, andvariably positioned abutment means positioned in accordance with theposition of said throttle valve forvarying the force of said resilientmeans.

6. in an ignition system for an internal combustion engine having aninduction passage with a throttle valve controlling the fiow of airtherethrough, the combination of an ignition distributor includingtiming means therein for controlling the timing of ignition, vacuumresponsive means for positioning said timing means, means for creating afirst vacuum in accordance with the velocity of air flow through saidinduction passage, means for transmitting said first vacuum to saidvacuum responsive means, engine vacuum responsive valve means for attimes directing engine vacuum to said vacuum responsive means, resilientmeans biasing said valve means in the closing direction, and meansresponsive to the position of said throttle valve for increasing theclosing force of said resilient means as said throttle valve approachesa substantially closed position.

7. In an ignition system for an internal combustion engine having aninduction passage With a throttle valve controlling the flow of airtherethrough, thet combination of an ignition distributor includingtiming means therein for controlling the timing of ignition, vacuumresponsive means for positioning said timing means, means for creating afirst vacuum in accordance With the velocity of air flow through saidinduction passage, means for transmitting said first vacuum to saidvacuum responsive means, engine vacuum responsive valve means for attimes directing engine vacuum to said vacuum responsive means, resilientmeans biasing said valve means in the closing direction, and variablypositioned abutment means positioned in accordance with the position ofsaid throttle valve for varying the force of said resilient means, saidresilient means being connected to said abutment means and said valvemeans in such a manner so as to be capable of being placed in a state ofcompression at certain periods of operation While being placed in astate of tension during other periods of operation.

it) 8. In an ignition system for an internal combustion engine having apassage with the throttle valve controlling the flow of air therethroughand an ignition distributor,

a control valve assembly having timing means therein for controlling thetiming of the ignition and pressure responsive means for positioningsaid timing means, said assembly comprising a first vacuum means forcreating a vacuum in accordance with the rate of air consumption of saidinternal combustion engine, conduit means for communicating said firstvacuum to said pressure responsive means, means for reducing the efiectof said vacuum on said pressure responsive means, second vacuum meansresponsive to a predetermined value of engine vacuum for communicatingsaid engine vacuum to said pressure responsive means, and meansassociated With said throttle valve and responsive to engine load forvariably determining said predetermined value of engine vacuum at whichsaid second vacuum means becomes operative for communicating said enginevacuum to said pressure responsive means.

References Cited in the file of this patent UNITED STATES PATENTS2,381,610 Mallory Aug. 7, 1945 2,473,805 Mallory June 21, 1949 2,475,717Ostling July 12, 1949 2,867,197 McCullough Ian. 6, 1959

